body {
  .box {
    width: 400px;
    height: 400px;
    border: solid 1px #ddd;
    margin: 200px auto;
    box-sizing: border-box;
    position: relative;
    .small-box {
      width: 100px;
      height: 100px;
      border: solid 1px #ddd;
      box-sizing: border-box;
      position: absolute;
      display: flex;
      justify-content: center;
      align-items: center;
      &:nth-child(1) {
        top: 25%;
        left: 25%;
      }
      &:nth-child(2) {
        top: 25%;
        left: 50%;
      }
      &:nth-child(3) {
        top: 50%;
        left: 25%;
      }
      &:nth-child(4) {
        top: 50%;
        left: 50%;
      }
    }
  }
}
